Get Key From All Sessions in File backend can fail on corrupted sessions
For some obscure reason, a file session can be corrupted (not well serialized). In this case, the script purgeCentralCache will abort and leave old sessions, because of this error:
Corrupted storable string (binary v2.8) at /usr/lib/perl/5.14/Storable.pm line 416, <F> line 155, at blib/lib/Lemonldap/NG/Common/Apache/Session.pm (autosplit into blib/lib/auto/Lemonldap/NG/Common/Apache/Session/_FileGKFAS.al) line 178
Our FileGKFAS sub should be able to bypass this and continue on other sessions.